In a world progressively suffering from information overload, simplicity in information design becomes a quality of increasing relevance. Simplicity in visual data presentations creates clarity that facilitates good decision-making. In decision-making, as elsewhere, we can’t make a silk purse of a sow’s ear. Mediocre visual data presentations have three unwanted effects. They cause decision makers to use more time than necessary digesting the information on hand, they hinder decision makers to understand problems and evaluate possible decisions, and they inspire decision makers to neglect available information in favour of unfounded guesswork. Simplicity in information design fights all three undesired effects. The simplicity in demand is functional simplicity. Functional simplicity in information design is concerned with improving usability and utility of information and should not be confused with minimalism, which is a matter of aesthetics. Functional simplicity in information design means more understanding with less reading. That in turn leads to more effective and more efficient decision-making. Functional simplicity in information design goes beyond raw reduction of data presentations. It involves size, variation/repetition, and structure. All three dimensions of simplicity influence the amount of redundancy that creates the delicate balance between necessity and superfluity, between understanding and boredom. The measure of redundancy that is both necessary and sufficient should be determined with a view to the context and the expected culture of the intended target groups. This paper pins down the concept of functional simplicity, discusses its importance in data designed for decision, and examines the three dimensions of simplicity one by one. Finally, it looks into the need for redundancy in several types of data presentations.